1. Field of the Invention
The present invention relates to a thermoplastic polymer composition which is superior in transparency, impact resistance, surface hardness, heat resistance, and gloss and with little warping
2. Description of the Related Art
Block copolymers comprised of conjugated dienes and vinyl aromatic hydrocarbons are superior in transparency when the content of the vinyl aromatic hydrocarbons is relatively high and provide a thermoplastic resin with better impact resistance than polystyrene. Accordingly, these block copolymers have increasingly been used in recent years in the fields of food packaging, sundry goods for daily use, toys, home appliance components, and the like. However, these block copolymers have the defect of being poorer than other plastics in their surface hardness and heat resistance.
On the other hand, polyphenylene ether resins are superior in dimensional stability, electrical characteristics, resistance to heat deformation under high loads, waterproofness, and the like and are therefore widely used in industry. However, such polyphenylene ether resins have the defect of being inferior in impact resistance and processability during molding.
Therefore, various attempts have been made to blend the two with the object of taking advantage of the respective merits of block copolymers comprised of conjugated dienes and vinyl aromatic hydrocarbons and polyphenylene ether resins and to compensate for their mutual defects.
For example, Japanese Unexamined Patent, Publication (Kokai) No. 48-62851 (i.e., DE-A-2255930) and Japanese Unexamined Patent Publication (Kokai) No. 51-129450 (i.e., GB-A-1532455) disclose normally rigid thermoplastic compositions comprised of (a) polyphenylene ether resins, (b) A-B-A' type elastomer block copolymers wherein the central block B has a molecular weight which is larger than the combined molecular weights of the end blocks A and A', and (c) styrene homopolymers or random copolymers. Further, Japanese Unexamined Patent Publication (Kokai) No. 52-125560 (i.e., GB-A-1522458) discloses a thermoplastic molding composition comprised of a homogeneous mixture of (i) a polyphenylene ether resin, (ii) a styrene resin, and (iii) a radial tereblock copolymer. Further, Japanese Unexamined Patent Publication (Kokai) No. 58-176240 discloses a thermoplastic resin composition comprised primarily of 1 to 20 parts by weight of a block copolymer comprised of 10 to 60 parts by weight of a vinyl aromatic compound and 40 to 90 parts by weight of a conjugated diene, based on 100 parts by weight of a modified polyphenylene oxide resin. However, the block copolymers used in these compositions are block copolymers having a content of the vinyl aromatic compounds of 60% by weight or less and these compositions are inferior in transparency, surface hardness, heat resistance, and gloss.
On the other hand, Japanese Examined Patent Publication (Kokoku) No. 54-27025 (i.e., U.S. Pat. No. 3,639,508) discloses a thermoplastic composition containing (A) 1 to 45% by weight of a polyallylene oxide and (B) 99 to 55% by weight of a block copolymer having 10 to 90% by weight of at least one type of monovinyl aromatic block. It describes a composition using a block copolymer with a content of the vinyl aromatic compound of 80% by weight. However, the composition has the problems of being inferior in impact resistance and susceptible to the occurrence of microcracks when bent. Further, Japanese Unexamined Patent Publication (Kokai) No. 61-223054 and Japanese Unexamined Patent Publication (Kokai) No. 62-70448 disclose impact resistant polyphenylene ether resin compositions containing (a) polyphenylene ether resins, (b) A-B-A' type block copolymers wherein the block B has a molecular weight that is smaller than the combined molecular weights of the blocks A and A,), and (c) an elastomer. However, these compositions have the problem that, while being superior in impact resistance, they are inferior in transparency and surface hardness.
Further, Japanese Unexamined Patent Publication (Kokai) No. 50-71742 (i.e., GB-A-1477706), Japanese Unexamined Patent Publication (Kokai) No. 53-94540 (i.e., GB-A-1559052) and Japanese Unexamined Patent Publication (Kokai) No. 56-95949 (i.e., U.S. Pat. No. 4,309,514) disclose compositions comprised of (a) polyphenylene ether resins, (b) styrene resins, and (c) hydrogenated block copolymers. However, the block copolymers used in these compositions have a content of the vinyl aromatic hydrocarbons of 60% by weight or less and are thus inferior in transparency, surface hardness, heat resistance, and gloss.